A "master" merged playlist.

[deckoff]

You can merge m3u files right now, but of course if you merge two files, the second one gets deleted.
You can also choose which url you want to keep by merging the files you don't want to keep with the file you want to keep.

So if you want to keep the link of Aaaa then you click the merge button next to the Aaaa file and say "merge with Bbbb". Then the Bbbb file disappers with its link and the data will be added to Aaaa.

If I understand you right, you want to keep the files Bbbb and Cccc even if you merged them with Aaaa.

Is that correct?

yes
Exactly that. Keeping all the playlists separate, AND getting a merged playlist at the same time. Also, this will allow to easily change which playlists will be merged.
Should be useful for people that might want to change the source of one or more of the playlists they have. I assume managing updates of more than one playlist will be easier.